The invention relates to a method of producing hydrothermally hardened products, by a reaction of a calcium-oxide product and a silica containing product, in the presence of at least one filler, by heating the material under steam pressure in an autoclave.
It is known per se that calcium oxide and/or silica containing products may undergo a chemical reaction as a result of a hydrothermal treatment, thus imparting mechanical strength to a product.
This mechanical strength may vary up to a compression strength of hundreds of kg/cm.sup.2, while the weight by volume of the products may vary.
The strength-imparting binding agent is produced from calcium oxide and silica containing materials during the time the mixture remains in an autoclave wherein a hydrothermal hardening process takes place. Sand may be used as silica containing material while calcium hydroxide is suitable as calcium oxide containing material.
The chemical reactions between the two materials proceed at the surface of the silica containing component, so that an indication of the specific surface as per BLAINE's determination supplies useful information when evaluating a sand or other silica containing material.
As is known, the composition of sand can be determined by a sieving-out process. Differences in the kinds of sand are, for instance, apparent from FIG. 1.
The width of the sieve opening or sand fraction is indicated horizontally, whereas the percentage of sand weight over a sieve opening of a certain diameter is indicated vertically.
Thus, according to the figure, 50% of the sand sample A is over the sieve opening having a diameter of 0.6 mm.
Line B represents a second, C a third, and D a fourth analysis.
On the other hand, triangle diagrams make is possible to show mixtures of three components, see FIG. 2. The components to be mixed are mentioned at the angles of the triangle, i.e. 100% 0-1 mm, 100% 1-3 mm, and 100% 3-5 mm. On the sides of the triangle, compositions may be indicated which are obtained by mixing for example the components 0-1 mm with the sand 1-3 mm.
Such a mixture may be indicated by a point S.
The size of the three fractions to be mixed in order to obtain P is to be determined in the following manner.
Three lines are drawn through point P which each run parallel to a side of the triangle.
These lines divide the sides of the triangle up into three segments.
The length of these line segments are then determinative of the composition of P.
Thus, P can be seen to be composed of:
25% fraction 3-5 mm PA0 25% fraction 0-1 mm PA0 50% fraction 1-3 mm
The size of the fraction 0-1 mm is read on the opposite side, i.e. on that portion of the side which is bounded by the points of intersection with the two lines through P.
This is line segment a.
The size of the fraction 3-5 mm is found in the same manner and is represented by line segment b.
Line segment c finally indicates the size of the fraction 1-3 mm in the mixture.
When considering the triangle to be the base of a prism, it is possible to indicate in this prism points which represent certain measured quantities of mixtures from the triangle.
For instance, a sand composition obtained by mixing has a certain specific surface. The size of this surface may then be represented by a point that lies within the space diagram.
FIG. 3 shows such a space diagram.
The base is a triangle at whose angles there are located again the fractions 0-1; 1-3 and 3-5 mm.
Perpendicular to this triangle there are erected at its angles the lines S-T and V, the final points providing for a plane STV, which in the drawing means interconnecting S, T and V by lines.
The length of the respective perpendicular lines, chosen in this case to be different, may be assigned for instance the value for the specific surface.
When the fractions are mixed, the mixtures will have specific surfaces lying between that of V and that of S.
The values for these specific surfaces can be found in the plane through S, V and T.
As it turns out, different mixtures are possible which have an identical specific surface.
These mixtures are found by imagining, at a given distance from the base, a plane that intersects the plane S.T.V.
In this imaginary plane, all points to the base, the triangle, are located at the same distance.
The line X intersecting with the plane S.T.V. lies within this imaginary plane.
It follows that the points of the line X are equidistant from the base and so have an identical specific surface. The mixtures comprised by this particular surface can be found by dropping perpendicular lines from the line X onto the triangle.
The line X is then found in the mixing triangle.
When moving the plane parallel to the base upwards, lines of intersection with the plane S.T.V. are obtained which all run parallel to X.
Since the distance from the base increases, however, the specific surfaces increase as well.
The graphical representation 3a shows once again the triangle diagram wherein there are shown the projections of the intersecting lines of the two planes in the case of the plane which runs parallel to the base being moved upwards.
These projections likewise run parallel to X.
The specific surface increases from X to X4.
The binding is brought about by calcium oxide and silica during the hardening phase.
The silica is available in limited quantities in the sand grain skin for the preparation of the agent.
The specific surface of a sand is, therefore, an indication of the amount of binding agent that can be formed.
If a particular sand should have a specific surface which is too small to enable conversion of all the lime during the hardening phase, it is useful to prolong the hardening time.
After such an extension of time, the compression strength will be found to have increased. This results from the fact that during the extended time of hardening the lime slowly penetrates through the reaction skin formed about the sand grain, and so is able to react with the silica. If, conversely, a particular sand has a large specific surface, the lime being present in small quantity, then the point at which the maximum amount of binding agent to be expected will have been prepared, will be reached more rapidly.
Therefore, a second important piece of information is the amount of active calcium oxide contained in a calcium oxide containing product used. The quantity of active calcium oxide is determined in the Netherlands as well as in other countries by means of the so-called "sugar method".
When mixing three components, such as ground phosphate rock with sand and a second kind of sand, it is possible to prepare a product with two kinds of sand (these materials to be indicated at the axes of FIGS. 1-4(b) so as to direct one's thoughts).
After all, the ground phosphate rock also contains sand that has a specific surface or that has a certain need for calcium oxide.
This need for lime, or rather the reactive surface with respect to the calcium oxide containing component may be determined by ascertaining the sugar-soluble calcium oxide content, after a hydrothermal treatment, which occurs in mixtures that were made with different percentages of calcium oxide.
It is apparent from FIGS. 2a and 2b that to build up the strength of the products formed it is necessary to be skilled in the art. FIG. 2a shows the strength of compressed mixtures of ground sand rich in quartz having a BLAINE fineness of about 850 cm.sup.2 /gram and a calcium hydroxide as a function of the total calcium oxide content. The maximum value of the strength is rather critical, that is, in order to obtain the maximum strength it is essential to properly choose the ratio between the amount of calcium oxide to be used and the amount of silica that can react with the calcium oxide.
Such a precisely adjusted mixture ratio is also apparent from FIG. 2b.
In this graphical representation the shape of the strength curve for mixtures of coarse gravel, sand, ground sand and hydrated lime is shown as a function of the total CaO content.
The specimens so obtained were produced by mixing much water with the mixtures and by subsequently pouring them into a mould which was left in position around the specimen during the hardening phase.
The graphs show furthermore the extent to which the strength values of the products formed differ.